The long term objective of this research is to understand balance control in static and dynamic tasks, specifically as it relates to the physiological and biomechanical constraints faced by the aging adult. Specific Aims include: I) To determine the limitations on response capabilities in older adults, and older adults with a history of falling, as compared to young adults, when confronted with threats to balance of varying magnitudes designed to elicit a variety of adaptive balance strategies; 2) To determine whether the balance strategies used by young adults, older adults, and older adults with a history of falling, during stance perturbations are generalizable to the conditions under which most people fall, that is, during locomotion; and 3) To determine if one of the contributing factors to loss of balance in older adults with a history of falling is the inadequate allocation of attentional resources for balance control during the simultaneous performance of multiple tasks. Specifically, we propose to compare the neuromuscular (electromyographic), behavioral (kinematic) and force (kinetic) recordings of the responses of young adults, healthy older adults and older adults with balance problems, during the following balance conditions: a) During quiet stance, and during walking, horizontal platform displacements of varying sizes and velocities will be given to the subjects, in order to determine their ability to use a variety of adaptive balance strategies. b) During quiet stance subjects will be asked to balance under a variety of sensory conditions (eyes open, eyes closed, normal support surface, support surface rotating with body sway) while performing a simultaneous secondary cognitive task, designed to compete with the postural control system for attentional resources. Stability will be compared when balancing with and without the simultaneous performance of the secondary task. The ultimate goal of this work is to understand the specific neural and musculoskeletal constraints that contribute to balance problems in the healthy older adult and the older adult with balance problems so that we might design better health maintenance and rehabilitation programs.